The efficiency of a conventional Swiss lever escapement mechanism is typically 35% or 40% at best. In such an escapement, the interaction between the escape wheel and the pallet lever, in the usual case of steel teeth on ruby pallet stones, generates considerable friction, and impairs the efficiency of the escapement.
EP Patent 13199427 in the name of SWATCH GROUP RESEARCH & DEVELOPMENT Ltd, incorporated herein by reference, proposed replacing this mechanical interaction with magnetic forces using repelling magnets, which greatly reduced losses through friction.
However, efficiency is intrinsically linked to the level of torque provided by the barrel, due to the design of the magnetic pallet lever escapement. Indeed, it is a constant force escapement, i.e. it theoretically always supplies the same energy to the resonator. A variable portion of surplus energy is dissipated in the rebounds of the magnetic escape wheel. The higher the input torque at the escape wheel, the higher will be the total power provided by the barrel, which causes the magnetic escape wheel to rebound longer. This phenomenon results in diminished efficiency of the escapement when the torque at the escape wheel is high.
With low torque, the portion due to wheel rebounds is low. The efficiency of the escapement is high, much greater than that of a conventional Swiss lever escapement.
With high torque, the portion due to wheel rebounds is high. The efficiency of the escapement is lower than with a low torque, and is at a level comparable to that of a conventional Swiss lever escapement.
EP Patent 2911015 in the name of SWATCH GROUP RESEARCH & DEVELOPMENT LTD discloses a timepiece escapement mechanism comprising a stop member between, on the one hand, a resonator, and on the other hand, two escape wheel sets each subjected to a torque. Each escape wheel set includes a track that is magnetized or ferromagnetic according to a period. The stop member comprises at least one magnetized or ferromagnetic pole piece, transversely movable with respect to the travel of one surface of the track. The pole piece or the track creates a magnetic field between the pole piece and the surface. The pole piece is confronted by a magnetic or electrostatic field barrier on the track just before each transverse motion of the stop member controlled by the periodic action of the resonator. The escape wheel sets are each arranged to cooperate alternately with the stop member and are connected to each other by a direct kinematic connection.
CH Patent 706209 in the name of MONTRES ROMAIN GAUTHIER SA discloses a watch movement including at least one barrel and one gear train for transmitting energy from the barrel to other elements of the movement. The gear train includes a reduction gear with a first transmission ratio of 1, a torque compensation system with a cam downstream of the reduction gear to compensate for the variation in torque supplied by the barrel according to the strain state of the barrel, and a gear system with a second transmission ratio greater than 1 for driving the other elements of the movement. The torque compensation system includes a chain arranged to be wound over less than one turn or to unwind about the cam depending on the strain state of the barrel.
EP Patent 1914604 in the name of GIRARD PERREGAUX SA discloses a movement including an energy source having an output torque that varies according to its state of charge, intended to maintain the oscillating motion of a mechanical oscillator by means of a going train including a compensation device, this latter having an input kinematically connected to the energy source and an output kinematically connected to the mechanical oscillator, and being arranged to transmit a substantially constant torque to the mechanical oscillator regardless of the state of charge of the energy source. This compensation device includes a cam have a periphery of variable radius extending substantially in one plane, the variations of the cam radius being a function of those of the output torque from the energy source, and further includes an intermediate connecting mechanism arranged to ensure a substantially slip-free kinematic connection between the cam periphery and the going train.